This invention relates to structures or elements comprising assemblies of plural interfitting members, wherein the interconnection of the constituent members is effected by resilient deformation of at least a portion of one or more of the members. In an important specific sense, the invention is directed to structures comprising a flat thin plate (first member) attached to a support, by fitting a relief section which borders that plate, on at least one part of its periphery, into a complementary relief section borne by a second member, via a temporary "elastic warping" (resilient deformation) of at least one of the two members in the assembly. This attachment is herein sometimes termed a "clipping attachment."
One illustrative use of such structures is as rigid, self-sustaining signs. For example, two thin-walled, shallow, resiliently deformable channel members of metal or plastic may be interfitted in facing parallel relation to each other (with the side flanges or legs of one channel member inserted between the side flanges of the other) to constitute a hollow, rigid element capable of being mounted to serve as a sign, with the letters and/or other characters of the sign applied to the exposed central web surface or surfaces of one or both of the channel members.
In order to get a tight clipping attachment and in particular to ensure that the two assembled members are not likely to glide lengthwise relative to each other in the assembled structure, it is necessary that, after assembly, at least one of the members retains some elastic warping which will create a securing force for the two interfitted members. Actually, the inside or male member, i.e., the one whose projecting side flanges or border sections ("clipping sections"), in relation to the surface of that member, are pushed towards the center, is submitted to a flexing couple which tends to create a convex warping, pushing the center of the male member backwards and outwards to the side opposite where the clipping sections project, whereas the other element is subjected to a concave warping, in relation to the side opposite where its clipping sections project. Considering the channel formed by a plate or channel member and on both its side edges by the projecting clipping sections, the channel of the male member tends to be closed back and the channel of the female member, fitting from the top, tends to be open. Thus, if the members bordered by the clipping sections are thin plates which, consequently, offer little resistance to flexion, these plates will, after clipping attachment, show a concave or convex warping of their outside surface i.e. the surface not facing the other plate. In known structures of the described type, this warping is all the more noticeable owing to the fact that the interlocking ridge where the clipping sections of the members clip is spaced from the plate's plane; that is to say, the clipped whole will have a bigger apparent volume.
This warping, even if it is slight, is prejudicial to the nice appearance of the plate surface, especially under oblique lighting.
Apart from this inconvenience, however, the clipping attachment of interfitted members presents several assets which mainly lie in the fact that when they are of adequate type, the clipping sections can be detached and, as far as appearance is concerned, absolutely no attaching device is visible. These two assets are particularly appreciated when dealing with sign posting likely to be periodically changed, e.g. tables bearing the names of people living in apartment houses, directional signs on show grounds, signs bearing the name and position of people in public offices, signs or billboards in advertising or in shops to show prices, or in purely aesthetic devices which involve different color boards that can be moved around as one wishes.
In these different examples, the plates (members) building up the visible surface, or front plates, must be light and thin. When they are fixed on their support by clipping, their folded edges on the clipping sections along a thin plate forming the complementary member, or when they are fixed on single clips occupying only parts of the front plate, they are likely to show the undesirable warping described above.